Cu-catalyzed Si-NWS grown on “carbon paper” as anodes for Li-ion cells

The very high theoretical capacity of the silicon (4200mAh/g more than 10 times larger than graphite), environmental-friendly, abundant and low-cost, makes it a potential candidate to replace graphite in high energy density Li-ion batteries. As a drawback, silicon suffers from huge volume changes (300%) on alloying and dealloying with Li, leading a structural deformation that induces disruption. The use of nanostructured silicon materials has been shown to be an effective way to avoid this mechanical degradation of the active material. In this paper the synthesis of silicon nanowires, grown on a highly porous 3D-like carbon paper substrate by CVD using Cu as the catalyst, is presented. The use of carbon paper allows to achieve remarkable loadings of active material (2-5 mg/cm2) and, consequently, high capacity densities. The silicon electrode was investigated both morphologically and electrochemically. To improve the electrochemical performance various strategies have been carried out. It was observed that a very slow first cycle (C/40), which helps the formation of a stable solid electrolyte interphase on the silicon surface, improves the performance of the cells; nevertheless, their cycle life has been found not fully satisfactory. Morphological analysis of the Si-NWs electrodes before and after cycling showed the presence of a dense silicon layer below the nanowires which could reduce the electrical contact between the active material and the substrate

on the use of copper based substrates for ybco coated conductors

It is well known that the recrystallization texture of heavily cold-rolled pure copper is almost completely cubic. However, one of the main drawbacks concerning the use of pure copper cube-textured substrates for YBCO coated conductor is the reduced secondary recrystallization temperature. The onset of secondary recrystallization (i.e., the occurrence of abnormal grains with unpredictable orientation) in pure copper substrate was observed within the typical temperature range required for buffer layer and YBCO processing (600–850 °C). To avoid the formation of abnormal grains the effect of both grain size adjustment (GSA) and recrystallization annealing was analyzed. The combined use of a small initial grain size and a recrystallization two-step annealing (TSA) drastically reduced the presence of abnormal grains in pure copper tapes. Another way to overcome the limitation imposed by the formation of abnormal grains is to deposit a buffer layer at temperatures where secondary recrystallization does not occur. For example, La2Zr2O7 (LZO) film with a high degree of epitaxy was grown by metal-organic decomposition (MOD) at 1000 °C on pure copper substrate. In several samples the substrate underwent secondary recrystallization. Our experiments indicate that the motion of grain boundaries occurring during secondary recrystallization process does not affect the quality of LZO film

Dust Mobilization Experiments in the Context of the Fusion Plants - STARDUST Facility

This paper deals with the dust mobilization in fusion facilities, in which the plasma disruptions induce an erosion of small particles causing external releases if accidents occur. In the ITER safety guidelines the administrative limits of 200 kg carbon, 100 kg beryllium and 100 kg tungsten inside the VV have been fixed to avoid the population evacuation in case of accident. The conservative assumption to mobilize all these dusts is adopted in the accident analyses. To support a less conservative hypothesis some experiments have been performed inside the STARDUST facility (ENEA Frascati laboratories, Italy). The ECART code has been used for blind simulations to validate the dust transport model implemented. The results match satisfactorily the experiments. The dusts used were carbon, stainless steel, tungsten and a mixed dust (C, SS, W). The experiments represent a LOVA due to a small or a large air leak through two different VV ports. The measured mobilization rate ranges from 0.03% to 100% of the total amount of dust. That means the mobilization is strongly dependent on the relative position between air inlet and dust location and that the dust mobilization assumptions in the accident analyses shall be reduced, in some cases of several factors

Dust mobilization experiments in the context of the fusion plants—STARDUST facility

This paper deals with the dust mobilization in fusion facilities, in which the plasma disruptions induce an erosion of small particles causing external releases if accidents occur. In the ITER safety guidelines the administrative limits of 200 kg carbon, 100 kg beryllium and 100 kg tungsten inside the VV have been fixed to avoid the population evacuation in case of accident. The conservative assumption to mobilize all these dusts is adopted in the accident analyses. To support a less conservative hypothesis some experiments have been performed inside the STARDUST facility (ENEA Frascati laboratories, Italy). The ECART code has been used for blind simulations to validate the dust transport model implemented. The results match satisfactorily the experiments. The dusts used were carbon, stainless steel, tungsten and a mixed dust (C, SS, W). The experiments represent a LOVA due to a small or a large air leak through two different VV ports. The measured mobilization rate ranges from 0.03% to 100% of the total amount of dust. That means the mobilization is strongly dependent on the relative position between air inlet and dust location and that the dust mobilization assumptions in the accident analyses shall be reduced, in some cases of several factors

6Li-enriched LiF films grown by thermal evaporation for neutron detection

The new generation of neutron detectors based on 6LiF thin films has been widely investigated in the last decades. The structure of polycristalline thin films has a significant impact upon their performance in neutron detectors, however the relationship between the physical properties of LiF-based thin films and their performance is still far from being completely understood. A systematic investigation of the role played by the growth conditions on the optical and morphological properties of thermally evaporated 6LiF thin films has been carried out by combining spectrophotometry, stylus profilometry and atomic force microscopy. A clear picture of the influence of film thickness and deposition temperature on transparency, porosity, roughness and grain size of polycristalline 6LiF thin films thermally evaporated on amorphous substrates has been obtained

Modelling approach of a devolatilization-combustion process in a well stirred reactor

Object of this work is the definition of the optimal operative parameters of an experimental industrial burner working in flameless conditions. To reach this objective the main steps are described in the following. First, a parametrical optimization of the carbon oxy-combustion process in pressurized environment was performed. When carbon is injected in the combustor in slurry form, the particles break due to the combined effect of the shear stress induced by the injected air swirled and of the particle devolatilization process. In this phase, the carbon volatile species evolves and, successively, burns. The optimization was carried out by analyzing the chemical species generated after the devolatilization and their dependency on the main operative parameters, like temperature and pressure, which rule the process. The analysis needs acquisition of chemical and physical knowledge about the phenomenon of devolatilization and was performed with a dedicated scientific software. The kinetic parameters of the devolatilization process were obtained by assuming a single step kinetic model and by using the Arrhenius equation to correlate the data. The simulated composition of the volatile species and the definition of the fundamental parameters of the combustor, necessary to study the feasibility of a plant at the industrial size, allowed to perform a sensitivity analysis for the evaluation of the most efficient kinetic configuration of the combustion. The analysis was carried out with a commercial CFD software appropriately tailored and the results of the simulations were validated against the analysis of solid and gaseous emissions. This work allows the definition of an acceptable configuration of the combustor and provides a new starting point for the development of the mild technology applied to coal combustion

Mechanochemically assisted low temperature synthesis route of the 1144 Ca-K Iron Based Superconductor

Among the Iron Based Superconductors, the so-called 1144 family attracts significant interest due to its high critical fields and critical current densities and to the stoichiometric nature of the compounds, disentangling the superconducting properties from the compositional homogeneity. Their practical application is partly hindered by the severe and strict synthesis conditions, complicated by high temperature (T > 900 °C) treatments of volatile and toxic elements. In this work, a milder synthetic approach to produce 1144 materials is proposed. A simple one-step High Energy Ball Milling treatment of the pure elements is coupled to a low temperature (i.e. 600 °C) thermal treatment to produce the superconducting Ca/K-1144 material, characterized by a good degree of homogeneity and critical temperatures higher than 30 K. The results here reported demonstrate the previously excluded feasibility of a simple and easily scalable lower temperature synthesis route for a Ca/K-1144 compound. We suggest that the intimate mixing and dispersion of the starting elements promoted by the mechanochemical treatment constitutes a key factor for the successful lowering of the synthesis temperature